TMJC 2025 H2 Chem P3 QP

CANDIDATE NAME CIVICS GROUP H2 CHEMISTRY 9729/03 Paper 3 Free Response 23 September 2025 2 hours Candidates answer on the Question Paper. Additional materials: Data Booklet This document consists of 30 printed pages and 2 blank pages. TAMPINES MERIDIAN JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION READ THESE INSTRUCTIONS FIRST Write your name and Civics Group in the spaces at the top of the page. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Answer all questions in the spaces provided on the Question Paper. If additional space is required, you should use the pages at the end of this booklet. The question number must be clearly shown. Section A Answer all questions. Section B Answer one question. A Data Booklet is provided. The use of an approved scientific calculator is expected, where appropriate. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use Percentage Paper 1 / 30 / 15 Paper 2 / 75 / 30 Paper 3 Section A 1 / 19 2 / 20 3 / 21 Section B 4 / 20 OR 5 / 20 Paper 3 Total / 80 / 35 Paper 4 / 55 / 20 Grand Total / 100

2 Tampines Meridian Junior College 2025 JC2 Preliminary Examination H2 Chemistry Section A Answer all the questions in this section. 1 (a) Describe and explain the trend in the thermal stabilities of the Group 2 carbonates. [2] ……………………………………………………………………………………………...……. ……………………………………………………………………………………….................. ……………………………………………………………………………………………...……. ……………………………………………………………………………………….................. ……………………………………………………………………………………………...……. ……………………………………………………………………………………………...……. ……………………………………………………………………………………….................. (b) Calcium carbonate is used in flue -gas desulfurisation applications to remove harmful SO2 and NO2 emissions from fossil fuels burnt in power stations. (i) Draw dot-and-cross diagrams to show the bonding in the molecules of SO 2 and NO2. [2] (ii) With reference to your answer in (b)(i), explain why the bond angle in SO2 is found to be 118 while that in NO2 is 134. [2] ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………...

3 Tampines Meridian Junior College 2025 JC2 Preliminary Examination H2 Chemistry [Turn over (c) Magnesium carbonate, MgCO 3, can be prepared in the laboratory by the reaction between magnesium chloride solution and aqueous sodium bicarbonate according to the equation: MgCl2(aq) + 2 NaHCO3(aq) MgCO3(s) + 2 NaCl(aq) + H2O(l) + CO2(g) Ho = + 107 kJ mol–1 So = + 360 J mol–1 K–1 (i) Explain why the reaction shows an overall positive value for So. [1] (ii) Calculate G, in kJ mol–1, for the reaction at 50 C. [1] (iii) Explain qualitatively how temperature affects the feasibility of this reaction. [2] ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... ⎯⎯ →

4 Tampines Meridian Junior College 2025 JC2 Preliminary Examination H2 Chemistry (d) High purity magnesium carbonate, MgCO3, is produced industrially at high pressure via a two-step process. step 1: Mg(OH)2 + 2CO2 Mg(HCO3)2 step 2: Mg(HCO3)2 MgCO3 + CO2 + H2O When 150 kg Mg(OH) 2 was reacted with excess carbon dioxide gas, and the resultant Mg(HCO3)2 vacuum dried to remove carbon dioxide and water, 168 kg MgCO 3 was produced. Determine the percentage yield of this industrial process. [2] ……………………………………………………………………………………………...……. ……………………………………………………………………………………….................. ……………………………………………………………………………………………...……. ……………………………………………………………………………………….................. ……………………………………………………………………………………………...……. ……………………………………………………………………………………….................. ……………………………………………………………………………………………...……. ……………………………………………………………………………………….................. ……………………………………………………………………………………………...……. (e) Titanium dioxide, TiO2, is a widely used white pigment employed to provide whiteness and opacity for paints, papers and toothpaste. Explain, in terms of structure and bonding, why carbon dioxide sublimes at –78 C while titanium dioxide is a crystalline solid with a melting point of 1840 C. [2] ……………………………………………………………………………………….................. ……………………………………………………………………………………………...……. ……………………………………………………………………………………….................. ……………………………………………………………………………………………...……. ……………………………………………………………………………………….................. ……………………………………………………………………………………………...……. ……………………………………………………………………………………….................. ⎯⎯ → ⎯⎯ →

5 Tampines Meridian Junior College 2025 JC2 Preliminary Examination H2 Chemistry [Turn over (f) The industrial manufacture of titanium dioxide involves reacting titanium( IV) chloride, TiCl4, with oxygen gas according to the equation as shown. TiCl4(l) + O2(g) TiO2(s) + 2Cl2(g) H1 o = – 136 kJ mol–1 (i) Define the term bond energy of Ti−Cl bond. [1] (ii) Using the  H1 o value given above and the data in Table 1.1, together with appropriate data from the Data Booklet, construct a fully labelled energy cycle and use it to calculate the average bond energy of the Ti−Cl bond in TiCl4. Table 1.1 enthalpy change of vaporisation of TiCl4(l) + 41 kJ mol–1 standard enthalpy change of formation of TiO2(s) – 945 kJ mol–1 standard enthalpy change of atomisation of Ti(s) + 471 kJ mol–1 [4] ……………………………………………………………………………………………...……. ……………………………………………………………………………………………...……. ……………………………………………………………………………………….................. ……………………………………………………………………………………………...……. ……………………………………………………………………………………….................. ……………………………………………………………………………………………...……. ……………………………………………………………………………………….................. ……………………………………………………………………………………………...……. ……………………………………………………………………………………….................. ……………………………………………………………………………………………...……. ……………………………………………………………………………………….................. ……………………………………………………………………………………………...……. ……………………………………………………………………………………….................. ……………………………………………………………………………………………...……. ……………………………………………………………………………………….................. ……………………………………………………………………………………………...……. [Total: 19] ⎯⎯ →

6 Tampines Meridian Junior College 2025 JC2 Preliminary Examination H2 Chemistry 2 Chromium is a hard, corrosion -resistant transition metal with variable oxidation states. It is widely used in energy-efficient and long-lasting redox flow batteries. One example would be the zinc dichromate battery, also known as the bichromate cell. The r eaction at one of the electrodes is given. Cr2O72– + 14H+ + 6e– 2Cr3+ + 7H2O The other electrode in this cell is the zinc electrode in the presence of H2SO4(aq) as the electrolyte. (a) (i) Construct the overall equation for the reaction when 1 mol of Cr 2O72– reacts with zinc. Use relev